The invention describes an angle-seating vane typically employed as shut-off or fluid throttling device in a butterfly valve. Butterfly valves of this kind usually employ flat and axis symmetric vanes to provide shut-off when squeezed into a vertical position perpendicular to the axis of the valve passage for example, if the valve passage is lined with an elastomer. Such vanes have a slightly larger diameter than that of the passage causing some of the elastomeric liner to be displaced. Such a system works well for valves only requiring on-off service but are not practical for throttling or modulating service, since the diametrical interference produces substantial friction resulting in a jerky action tending to upset a smooth fluid control.
Furthermore, repeated closures can lead to abrasive wear of the liner causing eventual leakage. Finally, flat butterfly disks or vanes are subject to substantial dynamic torque due to the suction effect imposed by the fluid on that portion of the vane facing downstream. Such high torque can lead to instability and requires strong and costly actuating devices to overcome.
My invention overcomes these and other objections by providing a vane which does not rely on diametric interference between vane and liner. This is accomplished by assuring shut-off through gentle touching of the liner by the outer rim of my vane at an angle whose tangent is larger than the coefficient of friction between the metal vane and the elastomer liner material, or a metal surface, thus assuring a gentle opening action.
Furthermore, my vane has a cup-shaped opening on the half portion facing downstream. This breaks up any suction effect by the passing fluid assuring a greatly diminished hydraulic torque effect.
The flat outer rim around a portion of the circumference provides a gripping surface, in order to facilitate a turning by a lathe or other machinery in order to machine a required precise diameter of my vane when in a tilted position.
This design is especially suitable for applications in the bioprocess industries requiring a germ-free environment. This is possible since this vane has no opening for the collection of germs or impurities (except for the shaft passage, which is sealed on either end).
Another advantage over current state of the art is the fact that the invented vane has a much more gradual opening flow characteristic. This vane has an elongated contact area with the valve's passage ending about 15 to 25 degrees from the vertical axis. Any 10 degree turn from the closed position will yield a flow area proportional to 1−cosine (10 degrees)=0.015 times the radius of the valve's passage. In contrast, conventional angle seating vanes have a contact angle of 15 degrees. In this case, a 10 degree turn will produce a gap proportional to 1−cosine (10+15)=0.09 times the radius of the passage. This is a 6 times improvement over the prior art.
There are a number of prior art patents, having vanes in order to reduce dynamic operating torque; Examples are U.S. Pat. No. 2,271,390 by Dodson and German patent 2430821. While patent 2430821 lacks the improved flow characteristic and machinability feature of the present invention, Dodson's vane has an excessive cross-section in order to provide a special dynamic profile. This limits the flowcapacity of his device severely. Furthermore, his gradual increase is compromised with an opening angle of 15 degrees. Brown, U.S. Pat. No. 2,278,421 has similar problems since one-half of his vane seats at about 45 degrees, which makes for an even more rapid opening.
U.S. Pat. No. 6,726,176 shows a more modern version of a tight shut-off butterfly valve employing a double eccentric vane. Here a desirable characteristic is achieved by utilizing a contoured portion as part of the vane and in the valve housing itself. Such solutions are impossible in lined or sanitary butterfly valves. The same patent also shows a cupped recess, in order to reduce dynamic torque (see FIG. 5). Its effectiveness is limited by the near flat surfaces between the upper and lower seats. In my invention, the fluid is guided into a recess by the upper half which is tilted downstream. Finally, this referenced invention lacks the machinability feature provided in my current invention by the upper and lower rims.